1. Field of the Invention
The present invention relates to a transformer and in particular to a transformer with different coil winding densities.
2. Description of the Related Art
Referring to FIG. 1, a conventional transformer 1 has two E-shaped iron cores 12 combined to form a closed magnetic loop. Further, the conventional transformer 1 has a bobbin 10 divided into a primary winding window 101 and several secondary winding windows 102 by the flanges 11. The secondary winding windows 102 are formed to prevent arcing faults due to high voltage difference between two adjacent layers of coils. A plurality of pins 103 are disposed at both ends of bobbin 10 for connecting the wire of the coils to a circuit board (not shown).
As the primary and secondary winding windows 101, 102 are disposed at different positions of the same bobbin 10, it is difficult to achieve a high coupling ratio due to the long distance therebetween. Referring to FIG. 2a, another conventional transformer 2 is provided with a first bobbin 21 with two E-shaped iron cores 23 passing therethrough, and a second bobbin 22 enclosing the first bobbin 21. A plurality of pins 211, 221 are respectively disposed on the first and second bobbins 21, 22 for connecting the wire wound thereon. Referring to FIGS, 2b and 2c, a primary coil 212 is evenly wound on the first bobbin 21, and a secondary coil 222 is evenly wound on the second bobbin 22 with a plurality of flanges 223 disposed thereon for preventing arcing faults.
As shown in FIG. 2d, the distance between the primary and secondary coils 212 and 222 is small, and the coils overlap such that the transformer 2 achieves excellent coupling ratio. The transformers, however, must be capable of achieving appropriate coupling ratios to meet specific electrical circuit requirements.